There are numerous ways to dry porcini mushrooms, a process that preserves their nutrients and allows them to be kept for much longer than when they are fresh. First, it is important to properly clean and cut them into smaller pieces if they are large. One of the easiest ways to dry porcini mushrooms is to leave them out in a room where warm, dry air is circulating, although this may not work in very humid conditions. Another method is to use the oven on a low heat setting. A final way is to use a food dehydrator, which can be purchased at a number of retail stores that sell small home appliances.
Porcini mushrooms that are to be dried should be fresh, with a firm texture and no signs of sliminess or mold. They should be cleaned using a damp cloth or paper towel, because immersing them in water will increase the moisture content and make drying more difficult. If the fresh mushrooms are very large, they can be sliced or chopped because smaller pieces will take less time to dry.
One very simple way to dry porcini mushrooms is to leave them out on a paper towel or paper plate and allow the room air to dry them. This method works best with smaller whole mushrooms or slices. The mushrooms will take a few days and as much as a week to dry completely and should be checked regularly for any signs of mold or rotten spots. A room with warm air, low humidity, and adequate circulation is the best place for drying porcinis in this way. Placing them next to a sunny window is also a good way to speed up the process.
If air drying is not feasible, another way to dry porcini mushrooms is in the oven. It is best to place them on a rack over a baking sheet so that air can circulate on all sides of the mushroom. The oven temperature should be on a low heat setting with the door left slightly open to allow air flow and help to prevent the mushrooms from burning. A convection oven can also work well for this purpose becausee it naturally circulates air. The mushrooms will take several hours to dry using the oven method and should be very brittle and break easily apart when they are fully dried. If any moisture remains, it can encourage the growth of mold and bacteria and the mushrooms will not be usable.
Using a food dehydrator is another simple way to dry porcini mushrooms. Many of these appliances have several racks to allow a larger quantity of food to be dried in one batch. They can be expensive, but can save money in the long run because they help to preserve mushrooms before they spoil. Most are simple to use and come with detailed operating instructions.